Spacewatch Observations of Asteroids and Comets with Emphasis on Discoveries by WISE

AAS/DPS Poster 13.22 Thurs. 2010 Oct 7: 15:30-18:00

Robert S. McMillan1, T. H. Bressi1, J. A. Larsen2, C. K. Maleszewski1,J. L. Montani1, and J. V. Scotti1

URL: http://spacewatch.lpl.arizona.edu 1University of Arizona; 2U.S. Naval Academy

Abstract

• Targeted recoveries of objects discovered by WISE as well as those on impact risk pages, NEO Confirmation Page, PHAs, comets, etc. • ~1900 tracklets of NEOs from Spacewatch each year.

• Recoveries of WISE discoveries preserve objects w/ long Psyn from loss. • Photometry to determine albedo @ wavelength of peak of incident solar flux. • Specialize in fainter objects to V=23. • Examination for cometary features of objects w/ comet-like orbits & objects that WISE IR imagery showed as comets. Why Targeted Followup is Needed

• Discovery arcs too short to define orbits. • Objects can escape redetection by surveys: – Surveys busy covering other sky (revisits too infrequent). – Objects tend to get fainter after discovery. • Followup observations need to outnumber discoveries 10-100. • Sky density of detectable NEOs too sparse to rely on incidental redetections alone. Why Followup is Needed (cont’d)

• 40% of PHAs observed on only 1 opposition. • 18% of PHAs’ arcs <30d; 7 PHAs obs. < 3d. • 20% of potential close approaches will be by objects observed on only 1 opposition. • 1/3rd of H≤22 VI’s on JPL risk page are lost and half of those were discovered within last 3 years.

How “lost” can they get?

• (719) Albert discovered visually in 1911. • “Big” Amor asteroid, diameter ~2 km. • Favorable (perihelic) apparitions 30 yrs apart. • Missed in 1941 due to inattention. • Missed in 1971 due to large uncertainty. • MPC recognized (719) as a rediscovery by Spacewatch in 2000.

1979 XB: A “Big” Lost “VI”!

• 4-day observed arc in 1979 December. • H ≈ 18.5 ↔ Diameter 370-1200 m. • Synodic period ≈ 1.4y. • Possible close encounters in 2056 & 2086. • Not rediscovered in >3 decades of modern surveying.

0.9-m Spacewatch Telescope

Hyperboloidal primary & refractive field corrector. 4-CCD Mosaic. Bandpass ≈ 0.5-0.9 μm; λeff ≈ 0.7 μm. Began 2003 April. 23 nights per lunation. Automated in 2005 May. Patterns near opposition, WISE regions, & low elongation in east in morning. 1400 deg2 per lunation. V mag limit ≈ 20.5-21.7 depending on conditions.

Spacewatch CCD Mosaic on 0.9-m telescope. Four EEV Grade-1, back-illuminated, antireflection-coated CCDs of 4608x2048 pixels each. 37 million pixels. 1 arcsec per pixel. 2.9 deg2 covered. Spacewatch 1.8-m Telescope: 0.6×0.6 deg FOV. Same bandpass & scale as 0.9-meter.

Has reached V=23.3 by shift & stacking, typical Vlim ≈ 22.3. Mostly drift scanning for smoother background & responsivity.

Stacking @ asteroid rate.

Spacewatch 1.8-meter telescope scans.

 Target ↑ Spacewatch Followup of WISE- observed objects as of 2010 Sep 1 • 226 out of 324 NEOs observed by WISE. • 54 out of 115 NEOs discovered by WISE. – V mags ≤ 22.9 • 10 out of 17 PHAs discovered by WISE. • 9 out of 16 comets discovered by WISE. – T mags ≤ 22.1 • 19 out of 33 Centaurs, SDOs, & other irregular objects discovered by WISE. Comet P/2002 LN13 = 2010 L2 (LINEAR) Comet P/2002 LN13 = 2010 L2 (LINEAR) Comet P/2002 LN13 = 2010 L2 (LINEAR) observed w/ Spacewatch 1.8-m on 2010 June 15. Integration time in 3 co-added images = 418 sec. North up; East to left. Image size 23.5 12.6 arcmin. Tail ≥2.8 arcmin in p.a. 248 deg. Tmag=20.3. Discovered by LINEAR in 2002 as 2002 LN13. WISE discovered a tail on 2010 June 10 which was confirmed by these images.

Number of NEOs Observed per Year The effects of the introduction of the 1.8-meter telescope in 2001, the mosaic of CCDs on the 0.9-meter telescope in 2003, the automation of the 0.9-m in 2005, and recent software enhancements are evident. Numbers of Different PHAs Observed by Project 2003 Jan 1 - 2010 Aug 24:

• Spacewatch = COD 691 + COD 291 118 • Catalina = COD's 703, G96, E12, 693 & 413 113 • LINEAR = COD 704 90 • Holmes = COD's H21 + H55. 60 • Lowell = COD 699 (LONEOS) & 688 (1.8-m) 30 • NEAT (JPL) = COD's 644 + 675 + 566 + 608 26 • Faulkes = COD's F65 + E10 22 • Klet = COD's 046 & 246 19 • Mauna Kea = COD 568 19 • Mt. Hopkins/CfA = COD 696 19 • Mt. John, New Zealand = COD 474 18 • McDonald Obs. = COD 711 18

Observations of PHAs, by Observatory >50d arc-lengthening PHA Followup Using Bigger Telescopes

• Target-of-Opportunity Mode  V=24. – KPNO 4-meter MOSAIC camera, FOV 35 35 . – WIYN 3.5-meter MiniMo camera, FOV 9 9 . – CTIO 4-meter Mosaic camera, FOV 35 35 . • Steward 2.3-m 90Prime camera, FOV ~1 deg2.

Minor Planet 2010 OM101 observed with the WIYN 3.5-m f/6.3 telescope on 2010 Sep 9 UT. High-e outer solar system object (trail) discovered Jul 28 by WISE showed no coma in 0.7 arcsec seeing while near perihelion. Observers A. L. Henry, M. A. Malkan, G. Will; Measurers A. Mendez, J. A. Larsen. Distribution of Absolute Magnitudes of Small NEOs • Spacewatch 0.9-m mosaic survey 2003-2010. • Detections of known + previously unknown NEOs. • De-biased for sky coverage & efficiency. • Extended knowledge of dist’n to H≈ 28. • Compare w/ dist’n of small craters on Moon. Cumulative Absolute Magnitude of NEOs Determined by de-biasing detections of NEOs with Spacewatch 0.9-m telescope and 2.9 deg2 mosaic that surveyed the ecliptic from 2003 Apr -2010 June. NEA Size Dist’n wrt Power Law extended to H=28 Acknowledgements

• The Spacewatch Team. • The NEOWISE Team led by A. K. Mainzer. • The IAU’s Minor Planet Center listings. • NASA’s NEOO & PAST Programs. • The Brinson Foundation, the estates of R. L. Waland and R. S. Vail, & other private donors.